Which one of the following halogen compounds is not useful as a substrate in an $S_N2$ reaction?

Which among the following compounds will undergo the fastest $S_{N}2$ reaction?

Rank the following compounds in order of decreasing rate of solvolysis with aqueous ethanol (fastest $\to$ slowest):
$(1)$ $CH_2=C(CH_3)Br$
$(2)$ $1-bromo-1-methylcyclohexane$
$(3)$ $CH_3-CH(Br)-CH_2-CH(CH_3)_2$

Arrange the following in order of their leaving group tendency:
$(I) Br^{-}$,$(II) CH_3COO^{-}$,$(III) CH_3CH_2O^{-}$,$(IV) PhO^{-}$

Which of the following is the correct decreasing order of the boiling point of the given compounds?

The major product obtained from the reaction of $CH_3CH_2CH(F)CH_3$ with $CH_3O^- / CH_3OH$ is ..........